1. Field of the Invention
This invention relates to disk drive suspensions, and more particularly to improvements in the mounting plates used to secure load beams to actuator arms. In the invention, positive coupling is obtained between the mounting plate and the actuator arms by defining cooperating locking structure on the respective components. The mounting plate thus does not rely merely on radial forces between the mounting plate boss and the actuator arm bore opening to engage the mounting plate and arm, as is conventional, but uses added structure to better ensure that there is no slippage between the arm and the load beam.
2. Related Art
Disk drive suspensions typically comprise a load beam carried on an actuator arm by virtue of the load beam base portion being welded to a mounting plate that is swaged into engagement with a bore in the actuator arm, e.g. as shown in U.S. Pat. No. 4,829,395. The mounting plate had a central, annular boss and a planar base surrounding the boss. The boss was swaged into the bore of the actuator arm for securing the load beam, attached to the mounting plate, to the arm. Originally, the mounting plates comprised machine-turned structures that of necessity were axially symmetric. Later, stamped versions were made that were identical in form, or nearly so, to the machine turned originals. Still later, designers took advantage of the stamping process to make extended mounting plate designs that were not axially symmetric.
Through all of this evolutionary change, the mounting plate design in use was an attempt to compromise staking integrity (torque-out), needed for secure connection of the load beam to the actuator arm, with gram load change, i.e. the change in the gram load imposed by the load beam in response to the staking operation. These two parameters were usually traded off against each other, so that improving one had a resulting degradation of the other, because of the nature of the staking operation.
The staking of the mounting plate to the actuator arm bore has been accomplished by swaging. In swaging, a series of steel balls of increasing diameter and all larger than the boss ID are pushed through the mounting plate annular boss to force the boss OD outward and into engagement with the surrounding bore of the actuator arm. This engagement provides a swaged joint. The tolerances of the stamped mounting plate and the actuator arm usually provide marginal retention (torque) values, i.e. resistance to slippage between the mounting plate boss and the arm bore.
The accepted method of determining swaged retention values is to test for rotational torque. A torque meter is attached to the stamped swage mount and rotated until the mount is displaced. Normally this test is done as an in process control operation. By adjusting the ball size, for a given combination of mount plate design and actuator dimensions, torque retention can be improved at the expense of gram load change. To assure torque values that are acceptable (10 in-oz or above) over a wide range of actuators sizes that may vary from the nominal design value due to manufacturing tolerance, a conservative approach would be to use a larger ball size than is absolutely necessary. This assures the worst case torque is sufficiently high. But, in this case the gram load change will be higher that desirable.
And, as drive size is reduced and the actuator becomes thinner and thus has a shorter boss height, the area of engagement is reduced and the retention torque becomes even less because the retention torque is proportional to the engagement length (defined as the amount of overlapping distance between the actuator and the boss of the mounting plate.